North Korea doubled down on iron exports to China in April, increasing the value of shipments to $20 million compared to $4.5 million during the same period last year, data from Beijing’s customs agency compiled by the Korea International Trade Association (KITA) shows.

The increase came as Chinese imports of prohibited North Korean commodities, such as coal, fell to zero for the first time since tighter UN sanctions were implemented in November last year.

North Korean iron is also subject to UN restrictions, though Resolutions 2270 and 2321 allow exports if their revenues go towards “livelihood” and not